In transmitting an audio or acoustic signal (which will be generally referred to as an “audio signal”) via an IP network or mobile communication, the audio signal is encoded to be expressed by a small bit count, the encoded data is divided into audio packets, and the audio packets are transmitted via the communication network. The audio packets received through the communication network are decoded by a receiver-side server, MCU, or terminal to obtain a decoded audio signal.
During the transmission of the audio packets via the communication network, a phenomenon can occur (so called packet losses) in which some audio packets are lost or errors are made in part of the information written in the audio packets. Such packet losses may occur because of a congestion condition of the communication network or the like. In such cases, the receiver side cannot correctly decode the audio packets and thus fails to obtain the desired decoded audio signal. Since the decoded audio signal corresponding to the audio packets subject to packet losses is perceived as noise, it significantly damages subjective quality for a human listener.